Engine control system use multiple variables for adjusting various engine operations. For example, an engine oil temperature (EOT) estimate may be used for calculating total friction and pumping losses at an engine, which in turn is used for torque control. As another example, EOT is used for powertrain limiting wherein an engine idle speed as well as a maximum and minimum permissible engine speed is limited to protect the engine from extreme temperature conditions (such as may occur when the EOT is too high or too low). EOT values may also be used for adjusting variable camshaft timing, controlling positive crankcase ventilation, and engine oil life monitoring.
Various approaches have been developed for EOT estimation. Some approaches rely on a direct EOT estimation via a temperature sensor coupled to an engine oil sump. Still other approaches rely on an (indirect) EOT inference logic wherein signals from various engine sensors, such as an engine coolant temperature (ECT) sensor, mature mass air flow (MAF) sensor, air charge temperature (ACT) sensor, etc., are combined with a last inferred EOT value stored in an engine controller's memory (e.g., in a keep alive memory or KAM) to generate inferred values during engine operation.
However, the inventors herein have identified potential issues with such approaches. As one example, in the direct estimation approach, degradation of the temperature sensor may cause the EOT measurements to become inaccurate. As another example, in the indirect estimation approach, degradation of any of the KAM, ECT sensor, MAF sensor, and ACT sensor (or any other such sensors being used in the EOT inference logic) can cause the inferred EOT value to be unreliable. Even when the sensors are functional, there may be conditions when the input from one or more sensors is not reliable for EOT estimation. As an example, during warm engine starts, the engine coolant may be significantly warmer than the engine oil. The engine controller may utilize a soak time (that is, the total amount of time passed since the moment the engine was turned off), the engine coolant temperature estimated by the ECT sensor, and a last estimated EOT value before the engine was turned off to calculate an initial EOT estimate for the EOT inference logic during the subsequent engine start. However, if either the soak time or the last estimated EOT value is corrupt due to a KAM error, then the initial EOT estimate may be inaccurate for at least the first several minutes of vehicle operation. As such, inaccuracies in EOT estimation can lead to sub-optimal engine performance. In addition, over-heating of the engine oil can lead to engine component degradation, and reduction of engine life.
The inventors herein have recognized that a temperature dependency of an oil control valve (OCV) of a variable camshaft timing (VCT) mechanism can be advantageously leveraged for reliable EOT estimation. For example, the relationship can be used to infer EOT when a sensor used in EOT estimation is degraded and/or when engine conditions render the sensor output less reliable. In one example, engine oil temperature may be estimated by a method for an engine comprising: adjusting an engine torque actuator responsive to engine oil temperature, the engine oil temperature formed from a mapped relationship stored in memory of camshaft solenoid duty cycle and camshaft angular velocity of a variable camshaft timing device.
As one example, an engine may be configured with an oil-pressure actuated VCT device that is actuated by a solenoid oil control valve (OCV). The VCT device may include an intake cam and an exhaust cam. Responsive to EOT estimation conditions being met, and one or more EOT faults being set, EOT estimation via a mapped relationship between camshaft solenoid duty cycle and camshaft angular velocity may be applied. The one or more EOT faults may include degradation of a sensor used to measure EOT (such as EOT sensor, an ECT sensor, an ACT sensor, etc.). The one or more EOT faults may alternatively include conditions where sensor output is not reliable, such as when the KAM is corrupted or during an engine warm-start. During such conditions, the controller may apply an excitation pulse to one of the intake and exhaust cam. For example, the controller may pass a current of a defined duty cycle pulse width through a solenoid of the OCV controlling the cams. The duty cycle may be selected so that the spool valve is moved to a position that directs engine oil to cam wheel pressure chambers, thereby rotating the cam wheel (in an advance or retard direction, as required based on the selected timing) relative to the camshaft. The controller may measure a change in camshaft speed or velocity (via a camshaft position sensor, for example) corresponding to the applied duty cycle and estimate a null duty cycle of the OCV in accordance. Based on the estimated null duty cycle, and further based on a mapped and calibrated relationship between angular velocity of the camshaft and solenoid duty cycle (e.g., mapped via an inverse model), the controller may infer an EOT. The estimated EOT may then be used to reliably estimate engine torque and actuate one or more torque actuators.
In this way, a reliable EOT estimate may be provided during conditions when sensors regularly used for measuring or estimating EOT are degraded, or when the output of such sensors is not reliable. The technical effect of relying on a mapped relationship between an applied duty cycle to an oil control valve (OCV) of an oil-pressure actuated VCT and angular velocity of the cam that the OCV actuates is that a more robust method of EOT estimation can be provided. By leveraging the temperature dependency of a resistance of the OCV in estimating EOT, the need for dedicated sensors is reduced, providing component reduction, and improving robustness of the approach to various EOT faults. By estimating EOT more reliably, torque estimation accuracy and engine torque limiting for temperature protecting is improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.